Method and apparatus for testing filament wire



July 28, L, MATSON 2,049,306

h METHOD AND APPARATUS FOR TESTING FILAMENT WIRE Filed Jan. 24, 1955RECORD/N6 GAL VA/VOMETM Ifiventor:

Louis L... Matson, J9 Fan/p15 19w 3 Atbornq Patented July '28, 1936METHOD AND APPARATUS FOR 'rns'rma I FILAM'ENT WIRE Louis 1.. Matson,East Cleveland, Ohio, assignor to General Electric Company, acorporation of New York Application January 24, 1935, Serial No. 3,301 4Claims. (01. 175-183) My invention relates tomethods and apparatus fortesting wire as to electrical resistance and is particularly applicableto the testing of wire of the type used as filaments for incandescentlamps 5 and similar devices. It is essential that such wire be extremelyuniform in resistance and therefore it is essential that the testingmethod and apparatus be very sensitive. My method and apparatus areparticularly adapted to furnish indicaio tions of the resistances ofvarious sections of a spool of wire which is preferably run through theapparatus and uniformity may be determined by a comparison of saidresistances. One of the preferred'features of my invention is theemploy- 15 ment of an instrument which makes a continuous record of saidresistances as the wire passes through the apparatus, said recordappearing as a line or curve and the more regular thesaid line, the moreuniform the wire. Other frtures and 20 advantages of my invention willbe apparent from the apparatus shown in the drawing and from thedescription thereof which follows. In the drawing Fig. 1 showsdiagrammatically an apparatus embodying my invention including 25 awiring diagram therefor.

The wire under test isindicated at It and comprises a portion extendingbetween the slots in blocks II and I2 and those in, blocks l3 and I.These blocks each hold a globule ii of mercury 30 within a well thereinwhich contacts the wire l and permits longitudinal \inovement thereof.In testing a relatively long length of wire, said wire is preferablymoved at a constant rate of speed and the readings of the testingapparatus recorded continuously. In such instances as shown, the wirepasses of! spool it through the mercury globules and onto spool II. Thetesting apparatus makes connection to the wire either directly throughthe mercury globules or through the 0 connection blocks holding theglobules.

In starting the test the section of wire between contact blocks II andI4 is connected in an elec-' tric battery circuit comprising batteryi3,resistances i3 and 20 and milliammeter 2| by 45 throwing switches 22and 23 into the up position. By the same movement of the switches theinner pair of contact blocks l2 and I3 are connected,

into the electrical Wheatstone bridge portion of the apparatus. Pairs ofcontact blocks are pref- 0 erably used so that the bridge connections tothe wire will be independent ofthe other connections made with thebattery circuit. Contact 1 block I2 is connected to the grid of thevacuum tube 23 and contact block I3 is connected to the '5 grid ofvacuum tube 23. The bridge circuit comprises the vacuum tubes 24 and 25,each in one half thereof, which have their filaments or cathodesconnected in multiple and in a circuit comprising battery'26 andrheostat 21. The voltmeter 28 is connected between the filament leads"which permits the rheostat to be adjusted so a known potential isapplied to said filaments. The rids of both vacuum tubes 24 and 25 areconnected to one of the filament leads, the former through the test wireand the battery circuit con- 1 nected thereto. The plates of tubes 24and 25 are connected through variable resistances 29 and 30 respectivelyto respective ends of the resistance of potentiometer 3|, the adjustablecontacting mechanism of which is connected to the battery 32. Thebattery 32 is also connected to the grid of tube 25 as shown. The testwire and the battery circuit connected thereto unbalance the bridgebecause of the negative grid bias produced thereby and the bridge mustagain be balanced since only changes in grid bias produced thereby aremeasured.- The bridge is balanced with the test wire in place byadjustment of potentiometer 3| and resistances 23 and 30, said balancebeing indicated either by the'galvanometer 33 or the recordinggalvanometer 34 which are connected between the plates of the tube asdesired by manipulation of switch 35. Plus and minus readings arepreferred, the zero being the mean for the wire. The specific recordinggalvanometer used is manufactured by the assignee and is of the type.disclosed in Patent 1,897,850 issued February 14, 1933.

If the resistance of the test wire is to be measured in standard units,switches 22 and 23 are 35 moved to the down position and the variableknown resistances 33, 31, 38 and 39 are adjusted until the galvanometerreads as before. The values of the resistances 36, 31, 38 and 33 arepreferably arranged in multiples of ten for con- 40 venience inadjusting and reading. The resistances 29 and an and potentiometer 3|are preferably of difierent values so as to provide different rates ofadjustment. The sensitiveness of the device is controlled by the batterycircuit which is connected to the test wire and the settings ofrheostats l9 and 20 therein are the controlling factors'thereof. Thesensitiveness of the device at any particular setting of the rheostatsmay be determined by switching from the test wire to the resistances 36,31, 33 and 33 and then comparing the galvanometer change for a givenchange in the known resistances. It is preferred that that portion ofthe circuit connected to the grid of vacuum tube 23 be grounded as shownat 43 and 56 nection to said wire, a source or electrical potenthat thecomplete device be shielded from outside interference. V v i What Iclaim as new and desire to secure by Letters Patent or the United Statesis: a

1. An apparatusior testingwire comprising a pair of spaced contacts formakin electrical con-' tlal connected through said contacts to thatportion oi. the wire tlferebetween, means for moving said wirelongitudinally so that all portions thereof are successively connectedto said source. a Wheatstone bridge connected to said wire through saidcontacts comprising a pair of vacuum tubes having grids, plates andcathodes, each connected in one arm thereof, a gaivanometer connectedbetween said plates, a mud source or potential having one lead connectedto saidplates and the other lead connected to said-cathodes and to thegrid of one of said vacuumtubes and a pair of variable resistances ineach or the leads between the plates and said second source of potentialforinitially balancing said bridge; said bridge being connected't'othe;wire under test through said contacts, one of which',iszconnected tothe grid of the other vacuum tube and the other or which is connected tosaid cathodes and caused to become unbalanced by non-uniform portions ofthe wire passing into position-between said contacts.

2. A method of testing wire which consists in adjusting the grid of athree-electrode vacuum tubebyusingthesaidwireasaslide wirepotentiometerso that the plate current of, said tube is balanced against the platecurrent of a second three-electrode tube having a bridge relation withrespect to the first tube, continuously moving the said wirelongitudinally and determining the degree oi unbalance between the'saidtwo tubes caused by the' variations in the resistance or successivesections or said wire. Y a

3. A method of testing wire which consists in impressing upon the gridof [three-electrode vacuum tube in one arm of a balanced electrical 10bridge an electromotlve force produced by the flow of current from abattery through the said wire, continuously moving said wirelongitudinally and determiningby the amountor unbalance of the saidbridge the variations in the resistanceof successive sections of saidwire. 4. An apparatus for testing wire comprising a pair of spacedcontacts rormaking electrical connection to'said wire, a source ofelectrical potential connected through said contacts to that portion ofthe wire therebetween, means for moving said wire longitudinally so thatall portions thereof are successively connected to saidsource' ofpotential, a Wheatstone bridge electrically connected to said wire andcomprising a pair or three-electrode vacuum tubes each connected in onearm thereof; 'means for initially balancing the bridge and means forindicating the degree 0! unbalance thereafter as non-uniform portions orthe wire pass between said contacts. so

LOUIS L. MATSON.

